Can you give an example? You are correct that there should always be something connected to the middle terminal of a potentiometer or there's no point in using one. However, it is possible that the point with no connection is one end of the potentiometer and not the wiper.

Allow me to demonstrate. First, imagine a voltage divider using two resistors as such:

It is called a voltage divider because the two resistors are literally dividing the voltage. If they are of equal value, the output voltage will be half of the input voltage. You've probably seen such diagrams and discussion before.

If you use the same model to think of a potentiometer, you will see that it is the same as a voltage divider made of two resistors, but the two resistors are variable like so:

As you turn the potentiometer, the wiper's connection moves along the total resistance and if R1 increases, R2 decreases, or if R1 decreases, R2 increases.

So if you see a potentiometer with one leg left unconnected, it is likely one of the ends and not the wiper arm. If you could point me to a schematic you are confused about I might be able to explain it better. In every potentiometer I've ever seen, though, it is the middle leg that is the wiper (unless it is an odd package like some of the long square precision trimmers or a slider). This is what one would look like if you opened it up:

So if you connect the wiper to one leg, you have just the variable resistance between the two. You can ignore the other leg if all you need is a variable resistance. It would be adjusting current flow much like a faucet would adjust water flow through a pipe.

Also, I'm not sure of the theory behind connecting the wiper to one leg, but essentially it is the same as leaving one leg unconnected (but might make a small difference... not sure). You'll have a variable resistance between one end and the wiper, but not a voltage divider. In that case it is considered a rheostat and not a potentiometer, but the name isn't too important.

Also, I'm not sure of the theory behind connecting the wiper to one leg

Leaving one end unconnected or conneced to the wiper both make the potentiometer a single variable resiistor.

My theory has always been that when the wiper stops making contact at least the resistance will not jump to infinity for the case where the wiper is connected to one end.

This may help for a circuit to at least keep it sort of working even when its broken really. Imagine a situation where an infinite resistor would cause a lot of noise or hum, or where it could drive the circuit out of specs possibly damaging it._________________Jan

That makes perfect sense. I was thinking about a theoretically perfect potentiometer that wouldn't break contact at the end, but you're right, most potentiometers will lose contact right at the end. This ensures a a maximum resistance equal to the potentiometer's value, rather than the possibility of an open or infinite resistance. Good call.

I was thinking about that wiper to one side idea just the other day! I came up with the same answer. I can't see any other possible reason for it._________________What makes a space ours, is what we put there, and what we do there.

yeassiree, just getting situated.. i got my workspace set up in a nice little 'nook' in my kitchen [1050$ in oakland=awesome apt] sos ill be getting back to work on my stuff real soon. met a nice gal in SF who has loaned me an oscilloscope [i sure do miss mine] and already got us a show in LA at the end of this month. lotsa stuff goin on around here.. enjoying it much!

yeah ifn i m able to make it out to the show ill let ya know, theres show this sat. here in oakland. ill get a link or somethinfg and PM it to ya

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